1. Field of the Invention
This invention relates to a light guide comprising a core of a methacrylic or acrylic resin and a cladding of a fluorocarbon resin firmly joined to the core. It also relates to a method for preparing the same.
2. Prior Art
Typical of currently available light guide tubes are tubes comprising a cladding in the form of a fluorocarbon resin tube which is filled with a liquid as a core. Since the core is liquid, the manufacture of these light guide tubes is complex. Such a light guide tube must be manufactured exactly to the necessary length because it cannot be cut to a desired length on use.
As to optical transmission media or cores, great attention is recently paid to plastic fibers because of ease of processing and low cost. The source material for forming plastic fibers which can serve as optical transmission media is mainly polymethyl methacrylate (PMMA). PMMA is well flexible as compared with quartz base glass fibers. More specifically, PMMA fibers having a diameter of less than about 1 mm are flexible. However, rods having a larger diameter have never been used as the light guide core.
We attempted to fill a cladding tube of a fluorocarbon resin with PMMA or a similar methacrylic or acrylic resin as the core. When a methacrylic or acrylic monomer was simply introduced into the fluoroplastic tube and polymerized in situ, the resulting methacrylic or acrylic resin was weakly joined to the fluoroplastic tube so that the light guide might not exert satisfactory optical transmission characteristics.
For improving the adhesion of a fluoroplastic member to another member, it is known in the prior art to treat the fluoroplastic member at its surface so as to be hydrophilic. Such conventional treatments on the member surface include mechanical roughening, chemical etching, metallic sodium treatment, and electric discharge treatment such as plasma and corona treatments. Among others, the plasma surface treatment is interesting as surface treatment on fluoroplastic members because it is clean and has a greater degree of freedom of surface modification. However, we found that simple plasma treatment of fluoroplastic members did not fully improve adhesion because fluorocarbon resins and methacrylic or acrylic resins were considerably different in surface energy. When a fluorocarbon resin layer was laid on a methacrylic or acrylic resin layer, delamination readily took place even on blunt bending. There is a need for a light guide tube wherein a fluorocarbon resin is firmly joined to a methacrylic or acrylic resin.